Starter for an internal combustion engine

ABSTRACT

The starter apparatus for an internal combustion engine (2) includes a starter-generator including a device for rotating a flywheel (5) to a predetermined rotational speed and a device for rotating the crankshaft (3) of the engine to directly start the engine; at least one clutch (6, 7) for directly coupling or disengaging the flywheel (5) with the crankshaft (3) of the engine (2) so that the flywheel (5) starts the engine (2) with the rotational energy stored in the flywheel (5) by the starter-generator in an impulse starting method and a changeover device (11) for changing between the impulse starting method based on engagement of the flywheel (5) with the engine (2) and a direct starting method in which the starter-generator (4) is directly coupled to the engine, wherein the changeover device switches between the direct starting method and the impulse starting method as a function of a temperature of the engine (2) so that the impulse starting method is used at comparatively lower temperatures and the direct-starting method is used at comparatively higher temperatures. The starter apparatus also includes a device for adaptively determining the threshold for changeover between impulse starting and direct starting.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a starter unit for an internal combustionengine having a starter and a flywheel which can be coupled to ordisengaged from the crankshaft of the engine with at least one clutch.

2. Prior Art

This type of starter unit is described in Patent Abstracts of Japan,Vol. 007, No. 199 (JP-A-58 098 658), in which a starter is connected tothe engine crankshaft via a pinion/toothed ring transmission.

For a starter system, there are essentially three main types ofapparatus:

1. Conventional electrical starter.

Such a design, because of the relatively brief attainable total servicelife of the starter motor and in particular its pinion, its toothedring, and its override clutch, as well as for noise reasons no longerleads to an embodiment with a promising future.

2. Starter-generator with direct starting.

Here the starter-generator is solidly connected to the crankshaft. Instarting, it acts as the starter motor, which is supplied by a battery,while during operation it acts as a generator for charging the battery.

Because of the necessary starting energy and starting power(approximately 150 Nm to 200 Nm of cold-starting torque for amedium-priced automobile) it is not feasible to use a starter generatorwith a typical 12 to 24 V lead starter battery. Furthermore, theelectric motor of the starter-generator would have to be enlarged bymore than a factor of 3 compared with what is needed for the generatorpower, which among other effects would also lead to problems in terms ofspace. For starting an engine at operating temperature, such astarter-generator would be unambiguously oversized.

3. Starter-generator with impulse starting.

For impulse starting, with the engine (and transmission) disengaged, theflywheel is first rotated up to a cranking rpm. As the clutch rapidlycloses, the flywheel then starts up the engine with rotational energy.

Recent vehicle concepts, optimized in particular with regard toenvironmental protection and fuel consumption, require the engine to beturned off at traffic lights; the current term for this is "start-stopmode". Moreover, the engine should be either merely disengaged, orpreferably turned off entirely when the engine is in an overrunningphase; the latter is accomplished by what is known as an "automaticinertia utilization transmission".

An application of this modern technology, however, means that the numberof starting cycles is increased by a factor of about 10, so that astarter that earlier was designed for 40,000 starting cycles not wouldhave to withstand from 400,000 to 600,000 starting cycles. On the otherhand, for reasons of comfort and also because an ever-greater number ofelectrically actuated accessories are being used, modern vehicles have agenerator power that is higher by up to a factor of 5 (previously, 1 to1.5 kW, and in future 5 kW and more). If the automatic inertiautilization transmission turns on frequently, still other problems arisein supplying the on-board electrical system.

In an embodiment according to German Patent DE 30 48 972 C2, the problemof generator power is solved in part by a generator installation on thecrankshaft, between the engine and the flywheel; if a manualtransmission is used, two clutches are then needed, which areadvantageously disposed in front of and behind the flywheel. With suchan arrangement, it is then possible with an automatic inertiautilization transmission to generate generator power.

Such an "impulse start" is suitable there for normal cold starts. Forre-starts, however, of the kind done with the engine warm at a trafficlight or at the end of an overrunning phase, it is unfavorable becauseof the time needed.

The same problem also exists in a design of the kind described in GermanPatent Disclosure DE 29 17 139. In this known starter unit, thecentrifugal mass of the crankshaft can be engaged and disengaged, and onslowing down, braking or in overrunning the engine can be allowed tokeep running by interrupting the drive train with a minimum rpm, such asthe idling rpm. In brief stops, for instance when stopped at a trafficlight, the drive train is also interrupted, but then the engine isturned off as well, while the flywheel continues to rotate and is thenre-engaged via the clutch to restart the engine. It is also possible ifthe flywheel rpm has dropped too far to use an electric motor toincrease the flywheel rpm again.

Overall, until now, in a crankshaft starter-generator concept, either anexcessively high starting moment for the cold start, as a direct startsystem, was definitive for designing the electrical machine and variousother electrical components, so that overall an appropriate compromisewould not be found, or if a classical starter or an impulse starter wasused, the demands for the re-starting with regard to starting time, lownoise level, wear and service life, for the high demanded number of400,000 cycles and more, could not all be attained.

SUMMARY OF THE INVENTION

The object of the invention is to overcome this disadvantage and tocreate a starter unit for an internal combustion engine thatautomatically selects the optimal starting method in all startingphases, and that can be changed over to the generator mode while theengine is running.

According to the invention a starter apparatus for an internalcombustion engine comprises

an starter-generator including means for rotating a flywheel to apredetermined rotational speed and means for rotating the crankshaft ofthe engine to directly start the engine without the flywheel;

at least one clutch for directly coupling or disengaging the flywheelwith the crankshaft so that the flywheel starts the engine with therotational energy stored in the flywheel by the starter-generator in animpulse starting method; and

changeover means for changing between the impulse starting method basedon engagement of the flywheel with the engine and a direct startingmethod in which the starter-generator is directly coupled to the engine,wherein the changeover means changes from the direct starting method andthe impulse starting method as a function of a temperature of the engineso that the impulse starting method is used at comparatively lowertemperatures and the direct-starting method is used at comparativelyhigher temperatures.

In the split according to the invention into different starting methodsvia the engine temperature, all the demands for a system designed for ahigh cycle number of 400,000 and more can be well-met. It is especiallyadvantageous that an economical overall solution is found by means of afast, low-noise direct start on the one hand and on the other by asomewhat more time-consuming but securely controllable alternativestart; in conjunction with an automatic transmission, an overallarrangement with only one clutch is also feasible in the proposedversion. It is particularly desirable that the start apparatus includemeans for triggering or controlling the starter-generator to reinforce asynchronization of the automatic transmission.

Advantageous further features of the subject of claimed invention willbecome apparent from the characteristics of the dependent claims andfrom the description and the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Two exemplary embodiments of the invention are shown in the drawing anddescribed in further detail in the ensuing description. In which:

FIG. 1, is a cross-sectional diagrammatic view through a starter unitfor use in a vehicle with a manual transmission; and FIG. 2 is across-sectional diagrammatic view through, a starter unit for use in avehicle with an automatic transmission.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A starter unit 1 for an internal combustion engine 2 engages acrankshaft 3 (drive shaft) and has a flywheel starter-generator 4, 5with an electrical machine, not shown in further detail, comprising astator and a rotor. Between the engine 2 and the flywheelstarter-generator 4, 5, a first (normal) clutch 6 is provided. A secondclutch 7 (drive clutch) is located between the flywheelstarter-generator 4, 5 and a manual transmission 8. The clutch 6 isequipped with a fast-closing servo 9.

A temperature sensor 10 is mounted on the engine 2 and reports thecurrent temperature to an electrical or electronic changeover device 11.The changeover device 11 sends temperature-dependent commands to thestarter-generator 4, in order to set it either for direct starting oralternative starting (impulse starting) with flywheel energy. A latentheat store 12 may be provided on the engine 2, to preheat the motor oil.

The alternative start is undertaken with the engine stopped, when itstemperature is below 50° C., for instance, and the direct start is donefor temperatures for instance over 50° C. For the very much lower numberof alternative starts (fewer than 200,000 cycles), an impulse start isperformed, in which the starter-generator 4, with the engine 2disengaged, first speeds up the flywheel 5 to a so-called "crankingspeed" of about 1200 rpm and then with the fast-closing clutch 6 startsup the engine via the rotational energy of the flywheel 5, thetransmission 8 remaining disengaged.

The requisite starting moment in the re-start is determined by therelatively low moments of friction and proportionately high compressionand acceleration moments at high temperatures. The starting moment canbe reduced by means of a preceding brief decompression phase. Since in adirect start this starting time is very brief (equal to 0.5 seconds orless), a brief overload on the electrical machine (starter-generator) isacceptable, resulting in a version that is optimized in terms of massand installation space. In each case the starting operation is trippedby applying a starting signal to the input 15.

FIG. 2, with the same reference numerals for corresponding elements,shows a similar starter unit 13 to that of FIG. 1. However, the secondclutch 7 is omitted, because the transmission is embodied as anautomatic transmission 14. The now full clutch 6 must be equipped withthe dynamic servo 9 for the impulse starting. The control system mustinclude gear synchronization and, on automatic gear shifting, astabilization of the engine rpm; that is, the components used anyway inthe automatic transmission 14 need merely be disposed differently andtriggered in a somewhat more complicated way.

For both models of FIGS. 1 and 2, it is true that for the alternativestart or impulse start the switchover from direct starting is dependenton the motor oil temperature and can be varied by preheating the motoroil, the consequence of which is to reduce the number of alternativestarts. Such oil preheating could be performed by means of the latentheat store 12.

It is also conceivable to introduce a brief decompression phase tofacilitate a direct start. It is also possible as an alternative startwith the engine cold to perform the startup of the crankshaft 3 by wayof the impulse start, that is, with the flywheel 5, and to reinforce theensuing runup via the direct start.

It is also advantageous to make a cranking rpm for the impulse startdependent on the ambient temperature of the engine 2 or on the oiltemperature.

In addition, a limit condition for the changeover from one startingmethod to the other can be ascertained adaptively.

Finally, in the use of the changeover device 11 of the invention, it isalso important that in conjunction with the components of an automatictransmission 14, only a single clutch 6 is necessary for the starterunit 13. In a preferred embodiment of the invention the starterapparatus includes means for reinforcing a synchronization of theautomatic transmission by triggering the starter-generator.

What is claimed is:
 1. A starter apparatus for an internal combustionengine (2), said starter apparatus comprisinga starter-generator (4)including means for rotating a flywheel (5) to a predeterminedrotational speed and means for rotating the crankshaft (3) of the engineto directly start the engine; at least one clutch (6, 7) for directlycoupling or disengaging the flywheel (5) with the crankshaft (3) of theengine (2) so that the flywheel (5) starts the engine (2) with therotational energy stored in the flywheel (5) by the starter-generator inan impulse starting method; changeover means (11) for changing betweenthe impulse starting method based on engagement of the flywheel (5) withthe engine (2) and a direct starting method in which thestarter-generator (4) is directly coupled to the engine; and means foradaptive determination of a threshold for changeover between saidimpulse starting method and said direct starting method; whereby saidchangeover means changes from the direct starting method and the impulsestarting method as a function of a temperature of the engine (2) so thatthe impulse starting method is used at comparatively lower temperaturesand the direct-starting method is used at comparatively highertemperatures.
 2. The starter apparatus as defined in claim 1, whereinthe means for rotating the crankshaft of the engine to directly startthe engine by the starter-generator (4) comprises means for directlyconnecting the starter-generator (4) to the flywheel (5) to drive theflywheel (5) and wherein the crankshaft (3) is coupled to the flywheel(5).
 3. The starter apparatus as defined in claim 1, wherein said enginecontains motor oil and said temperature is a temperature of said motoroil, and further comprising means for preheating said motor oil so thatthe number of alternative starting cycles is reduced by the preheatingof the motor oil.
 4. The starter apparatus as defined in claim 3,wherein said means for preheating said oil preheating comprises a latentheat store.
 5. The starter apparatus as defined in claim 2, furthercomprising means for setting up a brief decompression phase when theengine is started by the direct starting method.
 6. The starterapparatus as defined in claim 3, further comprising means for combiningthe impulse starting method and the direct starting method so that thecrankshaft (3) is rotated by the impulse starting method but at the sametime further torque is applied to the crankshaft by means of the directstarting method, whereby at least one of an impulse start of the engineand an ensuing run-up is reinforced via the direct starting method. 7.The starter apparatus as defined in claim 1, further comprising meansfor adjusting a cranking speed of said crankshaft as a function ofambient conditions of the engine (2) during the impulse starting method.8. The starter apparatus as defined in claim 1, further comprising anautomatic transmission and wherein said at least one clutch (6, 7)consists of only a single clutch (6).
 9. The starter apparatus asdefined in claim 8, further comprising means for reinforcing asynchronization of the automatic transmission by suitable triggering ofthe starter-generator (4).